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Posted by B. Davis on March 03, 2004 at 16:10:30:
In Reply to: Re: White Rogers 3-wire posted by Harold hydronicnetwork.net on February 25, 2004 at 07:55:43:
I had a similar problem -- I replaced an old Honeywell mechanical thermostat with an electronic one. At first, I opened up and rewired the thermostat to make it 3-wire valve compatible. That worked, but it was an ugly solution.
Later, I bought a simple relay that could be powered by the same 24 VAC that powers the zone valve. I used an Omron MJN2C-AC24, available from Digi-key (who absolutely rule, by the way):
http://www.digikey.com/scripts/DkSearch/dksus.dll?PName?Name=Z235-ND&Site=US
I also picked up a socket to make the installation look good. It's an Omron PTF21PC:
http://www.digikey.com/scripts/DkSearch/dksus.dll?PName?Name=Z253-ND&Site=US
Then, just wire the relay coil in series with your 2-wire thermostat and your 24 VAC power, and then use one of the two double-throw switches on the relay to control your 3-wire valve. This will look just like the old thermostat to your valve actuator.
It works great.
--B. Davis